1. Field of the Invention
The present invention is directed to a magnetic tape drive, of the type which receives a magnetic cartridge and which contains a magnetic read/write head.
2. Description of the Prior Art
Many types and structures of tape drives are known, which receive a magnetic tape cartridge therein so that the magnetic tape contained in the cartridge, when inserted into the tape drive, is positioned in front of a magnetic read/write head, or is at least positioned adjacent the read/write elements thereof.
Typically in such a magnetic tape cartridge, the tape is guided past an opening in the cartridge by tape guides mounted on the cartridge base plate. When the cartridge is properly inserted in the drive, this opening exposes a portion of the tape for engagement with the magnetic head to permit information to be written onto, and information to be read from, the magnetic tape as it is transported past the magnetic head. Data are stored on the magnetic tape in the form of a series of magnetic polarity reversals, in parallel tracks. Obviously, for a given tape width (width being measured in a direction perpendicular to the direction of tape transport), more data can be stored on a magnetic tape if the tracks are positioned as closely adjacent to each other as possible. Such close positioning (tight packing) of the tracks, however, requires high demands for correctly initially positioning the cartridge within the drive, and maintaining a precise position of the magnetic tape in the cartridge relative to the read/write elements of the magnetic head, so that data are not written into, or read from, an incorrect track due to misalignment between the tape and the magnetic head. The magnetic head is typically mounted on a mechanism such as a threaded, rotatable spindle, which allows the magnetic head to be moved vertically upwardly and downwardly in a direction along the tape width to read or write from track-to-track, or to position the magnetic head adjacent a specified track.
Many techniques and structures are known in the art for initially positioning the tape cartridge in the tape drive either in an exactly reproducible manner, or in an initially adjustable manner, so that when the tape drive begins operation, a reference or starting position of the tape cartridge, and thus of the magnetic tape itself, is known and can be entered into, or read by, the system which is used to move the position of the magnetic head during read and write operations. Such cartridge positioning, even if adjustable, is completed before the drive begins to operate, and this is status during operation. Even when the tape cartridge is accurately positioned at known reference points within the tape drive, however, the magnetic tape, which is slightly movable within the tape cartridge due to tolerances associated with the reels and tape guides, may nevertheless be canted or slanted as it is transported past the read/write elements of the magnetic head. Given closely packed data tracks on the magnetic tape, the slanting head-to-tape (misalignment) may be severe enough to cause writing or reading errors. Moreover, the mechanism which is used to vertically position the magnetic head also has tolerances and slippage associated therewith, which may also contribute to misalignment between the recording elements and the tape.
Moreover, in order to position the magnetic head, and thus the read/write elements thereof, at a selected track position along the width of the tape, reference signals are typically obtained from the tape itself in order to provide servo-control for positioning the magnetic head. For this purpose, the top or bottom of the tape can be monitored, and the magnetic head can then be positioned at a specified distance from the monitored edge at which the desired data track is expected to be located, given proper alignment between the magnetic head and the magnetic tape. Another known technique is to use a servo-track on, or embedded in, the magnetic tape for the same purpose, or one of the data tracks themselves can be arbitrarily designated as a reference track, and used for the same purpose. Typically, the magnetic head includes multiple read/write elements, and one of these read/write elements is used to monitor the servo-track, the reference track, or the tape edge, and one or more further read/write elements is used to conduct a read or write operation while appropriate positioning of the magnetic head takes place in a servo-loop. Again, if the tape is slanted as it passes by the magnetic head the servo loop may cause the magnetic head to be positioned at a track which is next to the intended track, or several tracks away if the misalignment is severe.
In tape cartridges of the type having tape guides therein, even when the cartridge is manufactured to very exacting tolerances, some small degree of play between the tape and the tape guides must still exist, so that the tape can move freely, at high speed, over the guides. It is therefore not possible, nor desirable, to mechanically restrain the tape to a sufficient degree to ensure that misalignment will not occur. Since every tape cartridge will have a slightly different amount of play inherent therein, many tape guides include elaborate adjustment mechanisms, or electronic adjustment procedures, which must be undertaken every time a new tape cartridge is inserted in a tape drive to arrive at the aforementioned static reference position. While such adjustment procedures are being conducted, the system is not available for data reading or data recording. Moreover, such conventional adjustment usually takes the form of trying to precisely adjust the position of the tape cartridge itself within the drive, under the assumption that if and when the tape cartridge is properly positioned, the tape itself then also will be properly positioned, or at least at a known position. It is also known to adjust the tape guides within the tape cartridge, relative to the base plate of the cartridge, or the tape guides within the tape drive relative to the head, for the same purpose. For the reasons discussed above, however, this conventional assumption is not correct, and there will likely always be some small amount of unknown deviation of the tape transport path from an xe2x80x9cidealxe2x80x9d transport path which would be precisely parallel to the cartridge base plate.
It is an object of the present invention to provide a magnetic data transfer system wherein head-to-tape misalignment is avoided, or at least significantly minimized, with a simple mechanical structure and without complicated electronics.
It is a further object of the present invention to provide a magnetic data transfer system wherein head-to-tape misalignment is avoided, or significantly minimized, by detecting misalignment directly at the magnetic tape itself.
As used herein, the phrase xe2x80x9cmagnetic data transferxe2x80x9d means reading and/or writing information onto and from a magnetic storage medium, such as a magnetic tape. Thus, a xe2x80x9cmagnetic data transfer head,xe2x80x9d as that term is used herein, means a head having electromagnetic, magnetoresistive or some other type of elements which are capable of reading data from a magnetic tape and writing data onto a magnetic tape, and encompasses the types of heads which are capable of performing both operations simultaneously, known as xe2x80x9creading while writingxe2x80x9d operation.
The above objects are achieved in accordance with the principles of the present invention in a magnetic data transfer system having a tape drive having a cartridge receptacle therein and also having a magnetic data transfer head disposed therein in a mount which allows vertical adjustment of the position of the magnetic data transfer head along a vertical adjustment direction. The magnetic data transfer system also includes a magnetic tape cartridge containing a magnetic tape which is received in the cartridge receptacle in the tape drive. When in this receptacle, the magnetic tape in the cartridge is movable by the tape drive in a transport direction past the magnetic data transfer head. The magnetic data transfer head is a two channel head, with each channel having a data transfer element, these data transfer elements being successively disposed along said transfer direction and monitoring a feature of the magnetic tape as the magnetic tape moves past the magnetic data transfer head. The monitored feature may be a position of a tape edge, a reference data track, or a servo track. Each of the data transfer elements, and thus each of the two channels, generates a signal dependent on monitoring of this feature. The magnetic data transfer system also includes an adjustment mechanism which mechanically engages either the cartridge in the receptacle, or the mount for the magnetic data transfer head, or tape guiding structure within the magnetic data transfer system or any combination thereof. A controller circuit is electrically connected to the adjustment mechanism for supplying a control signal thereto which operates the adjustment mechanism. The controller circuit is supplied with the respective signals from the two channels, and the controller circuit operates in the manner of a feedback circuit to control the alignment mechanism, via the aforementioned control signal, so as to minimize any difference between the respective signals from the channels. Any difference between the respective signals from the channels results from head-to-tape misalignment, since the aforementioned data transfer elements are disposed in succession along the tape transport direction. Therefore, minimizing the difference between these respective channel signals results in the adjustment mechanism operating to maintain the aforementioned vertical adjustment direction perpendicular to the tape transport direction, thereby avoiding or significantly minimizing any head-to-tape misalignment which may arise.
In an embodiment, the adjustment mechanism can include a height adjustment device which is disposed to engage and move magnetic head arrangement relative to the cartridge base plate, or to move the cartridge base plate relative to the head arrangement, dependent on the control signal received from the controller circuit. Which of these components is engaged and moved depends on which is mounted in a fixed manner, the non-fixed component being the one that is engaged and moved. The inventive principle is the same regardless of which component is moved. For example, the cartridge base plate in this embodiment can be inserted into the tape drive so that one end, or one side, thereof is disposed at a fixed azimuthal reference point, and the opposite end or side of the cartridge base plate is movable by the height adjustment device. The operation of the height adjustment device causes the cartridge base plate to pivot at the fixed azimuthal reference point, thereby slightly adjusting the angle of the tape in the cartridge relative to the magnetic head, so as to avoid or minimize any head-to-tape misalignment.
In another embodiment, the adjustment mechanism operates on tape guides, such as are adjustably mounted in the magnetic data transfer system (drive), and which define a tape transport path relative to the magnetic data transfer head. The guides can be vertically (azimuthally) moved relative to the magnetic head arrangement, for example.
In another embodiment, the adjustment mechanism can operate on the rotatable spindle on which the magnetic head is mounted. Typically, the aforementioned vertical adjustment of the magnetic head is accomplished by a threaded spindle, which proceeds through a threaded bore at a rear of the magnetic head. The threaded spindle is rotatable so that the magnetic head is thereby raised or lowered along the vertical adjustment direction dependent on the amount of rotation of the threaded spindle. The ideal vertical orientation of the threaded spindle is referred to as the zenith direction, and in this embodiment the adjustment mechanism includes a spindle adjustment device which acts on the spindle to move the spindle through positive and/or negative angles relative to the zenith direction. The spindle adjustment device can act on one side of the spindle, and the other side of the spindle can be acted on by a spring. Such a spring is commonly present in any event, as an adjustable zenith guide. The bottom end of the spindle is pivotably mounted in the tape drive to allow movement thereof at angles relative to the zenith.